1. Field of the Invention
This invention relates to anatomically shaped dental impression trays formed of thermoplastic material which may be directly molded within the mouth or on a male model and to a method of taking dental impressions of oral tissue, dental appliances, or dental prostheses using these trays.
2. Prior Art
To form a final impression of a dentulous or edentulous alveolar ridge, in the course of producing a male model of desired oral tissues, conventional practice involves the use of commercially available initial impression trays for use with either the maxillary or the mandibular alveolar ridges and contiguous tissues, in either dentulous or edentulous cases. These trays are available in a range of sizes so that one which makes an approximate fit with the patient's mouth area may be chosen for use. They have a cross-section characterized by a base with two normally extending walls so that they will surround the ridge of which an impression is to be formed. The contours of these trays are not anatomical in the sense that they are adapted to abut or lie in close proximity to the gum area surrounding the ridge, but rather a tray is chosen which fits within the patient's mouth and loosely surrounds the tooth or gum section. These stock trays are typically formed of aluminum or other material that may be bent or trimmed at the edges to improve the fit to an individual patient. Impression material is placed in the tray and a female cast of the required area is formed. This cast is then typically used to form a male model of the patient's mouth section either in the dental office or in a separate dental laboratory. The laboratory or dental office then uses this male model to form a custom final impression tray out of a plastic material. This tray is anatomical in that it closely adapts to the male model and is relieved in the muscle attachments and other contiguous tissue areas.
The dentist then uses this custom tray to form a final impression of the required area by placing a high definition, settable, impression material such as alginate, silicone, or polysulfide or the like, into the impression tray.
This conventional practice typically requires two procedures and is relatively expensive. Additionally, the stock impression tray may cause discomfort to the patient because of its relatively gross fit and inaccuracies creep into the procedure because of the multiple transfer steps.
A number of alternative means for forming final impressions have been proposed to overcome these recognized inadequacies of the conventional procedure. For example, several forms of stock trays have been devised which may be shaped exteriorly of the mouth to improve the accuracy of initial impressions. Deuschle et al U.S. Pat. No. 3,473,225 discloses such a stock tray formed of a thermoplastic sheet which can be heated exteriorly of the mouth and molded to improve its fit to the mouth. Similarly, McAdoo U.S. Pat. No. 3,654,703 discloses a stock tray made of plastic which is apparently pliable at body temperature and can be modified to better conform to the mouth.
Several arrangements have been proposed for elimination of the initial impressions altogether and formation of a final impression tray directly in the patient's mouth. Kinsley Pat. No. 1,955,709 discloses an impression tray formed of a woven metal matrix with a soft pliable covering that may be contoured directly to the patient's mouth. Similarly, German Pat. No. 885,772 discloses a process for making final impressions which does not use a tray for the impression material but rather employs an impression material which may be molded into a tray-like shape and then conformed to the mouth.
Each of these alternatives has certain deficiences. The non-anatomical trays which are moldable to better conform to the patient's intraoral anatomy still require formation of a male model and the creation of a final, anatomical impression tray using that model. The soft compliable final impression trays are susceptible to deformation as they are removed from the patient's mouth. The process suggested in the German patent suffers from the lack of the material which can form a self-supporting tray yet take a high definition registration of the tissue area.